Metal powder for additive manufacturing

Abstract

The purpose of the present invention is to provide a metal powder which contains a small proportion of needle-like particles, is suitable for an additive manufacturing device of a deposition method in which the powder is supplied from a nozzle, and to provide a metal powder for additive manufacturing in which the amount of the needle-like particles contained in the metal powder is less than the amount of the needle-like particles contained in the metal powder, based on the number of all the particles constituting the powder. The ratio of the number of particles having an aspect ratio of 0.4 or less and a maximum major diameter of 150 [mu] m or more is 0.30% or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a metal powder suitable for metal additive manufacturing. In particular, to a metal powder suitable for metal additive manufacturing of a deposition method. BACKGROUND

[0002] In recent years, when a shaped body composed of a metal is produced, a metal additive manufacturing method is applied. Among representative methods of the metal additive manufacturing method, there are a powder bed method (a powder bed fusion method), a deposition method (a directed energy deposition method), and the like.

[0003] In the powder bed method, by irradiation of a laser beam or an electron beam, a portion of a laid metal powder that is irradiated is melted and solidified. Through melting and solidification, metal particles are combined with each other. Irradiation is performed selectively on a part of the metal powder, and a portion that is not irradiated is not melted, and only the portion that is irradiated forms a combined layer.

[0004] On the combined layer formed, new metal powder is laid again, and irradiation of a laser beam or an electron beam is performed on the metal powder. In this way, by irradiation, metal particles are melted and solidified, and a new combined layer is formed. In addition, the new combined layer is also combined with the existing combined layer.

[0005] Through melting and solidification by sequentially repeating irradiation, a collection of combined layers gradually grows. Through this growth, a shaped body having a three-dimensional shape can be obtained. If such an additive manufacturing method is used, a shaped body of a complex shape can be easily obtained. As an example of the additive manufacturing method of the powder bed method, refer to Patent Literature 1.

[0006] In the deposition method, a laser is used as a heat source, and metal powder is sprayed from a nozzle toward a laser condensing portion, and the metal powder is melted and stacked. As an example of the additive manufacturing method of the deposition method, refer to Patent Literature 2.

[0007] In order to develop a powder suitable for metal additive manufacturing, attempts have been made in improving the characteristics of the metal powder such as laser absorption rate, inclusion concentration, fluidity, and the like. In the powder bed method, from the viewpoint of uniformly laying the metal powder, and in the deposition method, from the viewpoint of continuously supplying the metal powder from the nozzle, and the like, the fluidity of the metal powder is one of the most important characteristics.

[0008] The Japanese Industrial Standard (JIS) Z2502:2020 specifies methods for measuring the fluidity of metal powders. JIS metal powder fluidity is evaluated by measuring the time (s / 50g) required for 50g of powder to fall from a sample-filled funnel. Generally speaking, the more spherical the particles in a powder are, the higher its fluidity. Therefore, efforts are underway to improve the sphericity of powder particles as much as possible to enhance the fluidity of powders used in metal additive manufacturing. Furthermore, methods have been proposed to improve the fluidity of metal powders by mixing nanoparticles to reduce the adhesion between the particles (see Patent Document 3).

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent No. 4661842

[0012] Patent Document 2: Japanese Patent Application Laid-Open No. 2015-196264

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 2021-75784 Summary of the Invention

[0014] Problems to be solved by the invention

[0015] Generally speaking, the particle size range of metal powder used in the deposition method is 45 to 150 μm, which is larger than the particle size range of metal powder used in the powder bed method (10 to 45 μm).

[0016] In the deposition method, the metal powder must flow under its own weight within a capillary tube to eject the powder from the nozzle, making the powder's fluidity crucial. Low powder fluidity can lead to clogging of the tube during the process, preventing proper powder supply to the laser melt zone and potentially interrupting the forming process.

[0017] The evaluation of the fluidity of metal powder specified in JIS Z2502:2020 is a method that uses a small amount of 50 g as a sample and is therefore not a method that can actually fully evaluate the fluidity required for a deposition method.

[0018] To avoid interruptions in the forming process in deposition-based additive manufacturing equipment, powder must flow smoothly through the nozzle for several hours. However, in reality, even highly spherical and fluid metal powders may not flow properly through the delivery nozzle during long periods of additive manufacturing in deposition-based additive manufacturing equipment, leading to nozzle clogging and the need to interrupt the forming process.

[0019] Therefore, the inventors of the present invention found that the nozzle blockage was accumulated in the blockage. Figure 1 Needle-shaped particles with a major axis diameter of approximately 300 to 800 μm can accumulate in the powder discharge section during prolonged powder delivery, potentially causing nozzle clogging. Furthermore, the nozzle outlet diameter of the powder discharge section is typically equal to or slightly larger than the major axis diameter of the needle-shaped particles. Therefore, considering the flowability of such particles over such long periods of time in actual operation, clogging caused by needle-shaped particles is a known problem.

[0020] During the production of metal powders (e.g., atomized powders), needle-shaped particles do not always occur; they are generated unexpectedly and unintentionally. Classification of metal powders generally removes most of these needle-shaped particles by screening. Therefore, the majority of these particles are removed. Since the proportion of needle-shaped particles decreases after classification compared to before classification, it was previously believed that classification effectively eliminated them. This is because classification results in a value that has no effect on the fluidity (s / 50g) specified by the JIS. However, since the JIS fluidity is evaluated using a small amount of powder, such as 50g, it is not suitable for evaluating minute amounts of needle-shaped particles fed through a nozzle over an extended period. Accurately assessing the unexpected incorporation of minute amounts of needle-shaped particles using JIS methods for evaluating small amounts of powder is difficult, making it challenging to assess. Consequently, the incorporation of extremely small amounts of needle-shaped particles has not been fully recognized or studied.

[0021] However, in a deposition method that flows metal powder through a nozzle for a long period of time, even a very small amount of needle-shaped particles can accumulate in the nozzle over time, causing clogging. Therefore, there is a need for a metal additive manufacturing powder that minimizes the unintended generation of needle-shaped particles.

[0022] Therefore, an object of the present invention is to provide a metal powder having a low content of needle-shaped particles, which is suitable for a deposition-type additive manufacturing apparatus in which the powder is supplied from a nozzle.

[0023] Means of solving the problem

[0024] As a result of intensive research, the present inventors have developed a metal powder for additive manufacturing that has a low content of needle-shaped particles and is less likely to cause nozzle clogging, based on the viewpoints described below.

[0025] The present inventors and others have found that one of the reasons that needle-shaped particles in a powder pass through the screen mesh of a screen having a mesh size smaller than the long axis diameter is that the needle-shaped particles in the powder change their posture and stand up due to the application of strong vibration to the powder at the time of classification. If the needle-shaped particles stand up, the short axis diameter, which is smaller than the mesh size, of the needle-shaped particles faces the direction of the screen mesh, and thus the needle-shaped particles pass through the screen mesh in a standing position (see Figure 2 ).

[0026] When classifying a powder by a general vibrating screen device, a bouncing ball made of urethane rubber is loaded on the screen. When classifying a powder by the vibrating screen device in a state in which the bouncing ball is not used or the number of the bouncing ball is reduced, the vibration is suppressed, and thus the needle-shaped particles are not strongly vibrated as compared with the case in which the bouncing ball is used. Therefore, (1) in a state in which the bouncing ball is normally used, after a powder of a prescribed particle size is obtained by sequentially performing sieving by a vibrating screen device using a plurality of screens having different mesh sizes, (2) sieving is performed on the obtained powder by a vibrating screen device using a screen having a slightly larger mesh size in a state in which the bouncing ball is not used or the number of the bouncing ball is reduced. Thereby, the needle-shaped particles are suppressed from standing up due to vibration, and thus the needle-shaped particles remain horizontally on the screen having a slightly larger mesh size, and the powder of a prescribed particle size passes through the screen mesh without being clogged. Therefore, it is possible to efficiently remove only the needle-shaped particles.

[0027] Thus, the present inventors and others have reached the following recognition. If the vibration applied to a powder is suppressed by not using a bouncing ball or extremely reducing the number of the bouncing ball, and thus the needle-shaped particles are suppressed from standing up, a metal powder for additive manufacturing in which the needle-shaped particles are extremely small can be appropriately obtained after classification by a screen.

[0028] To solve the aforementioned problems, the present application provides the following metal powder for additive manufacturing.

[0029] [1] A metal powder for additive manufacturing, wherein the proportion of the number of particles having an aspect ratio of 0.4 or less and a maximum diameter of 150 μm or more, based on the total number of particles constituting the powder, is 0.30% or less.

[0030] [2] The metal powder for additive manufacturing according to [1], wherein the maximum value among the maximum diameters of the total particles constituting the powder is 1000 μm or less.

[0031] [3] The metal powder for additive manufacturing according to [1] or [2], wherein the proportion of the number of particles having an aspect ratio of 0.4 or less and a maximum diameter of 150 μm or more, based on the total number of particles constituting the powder, is 0.01% or more.

[0032] The present invention also provides a method for producing metal powder for additive manufacturing, comprising the following steps: sieving the metal powder sequentially using a vibrating screen device using a sieve with large mesh size and a sieve with small mesh size, while bouncing balls are normally used; and further sieving the metal powder using a vibrating screen device using a sieve with mesh size larger than or equal to that of the vibrating screen device, without using bouncing balls or with a reduced number of bouncing balls, to produce a metal powder having an aspect ratio of 0.4 or less and a maximum major diameter of 150 μm or greater, wherein the proportion of the number of particles constituting the total number of particles of the powder is less than 0.30%. By utilizing the difference in vibration caused by the presence or absence of bouncing balls, needle-shaped particles can be effectively removed.

[0033] Effects of the Invention

[0034] The metal powder for additive manufacturing of the present invention has excellent long-term fluidity. Therefore, when the metal powder for additive manufacturing of the present invention is used for additive manufacturing, for example, even in an additive manufacturing operation in which a nozzle is continuously used to supply powder in a deposition method, the additive manufacturing operation can be continued for a long time without the powder clogging the nozzle during the process. In addition, when the metal powder for additive manufacturing of the present invention is used for additive manufacturing, a dense molded body with low porosity can be obtained. In addition, if the maximum value of the maximum major diameter of all particles constituting the metal powder for additive manufacturing of the present invention is set to 1000 μm or less, a dense molded body with low porosity can be obtained, and stable fluidity can be continuously ensured during molding, which can further reduce nozzle clogging. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This figure shows a secondary electron image of needle-shaped particles in a Ni-based alloy powder captured by a scanning electron microscope (SEM).

[0036] Figure 2 These are diagrams explaining the phenomenon of upright needle-shaped particles passing through the mesh (slits) of a sieve used for classification. (a) is a schematic diagram viewed from above, and (b) is a schematic diagram viewed from the side. DETAILED DESCRIPTION

[0037] Hereinafter, the metal powder for additive manufacturing according to the present invention (hereinafter referred to as “the metal powder according to the present invention”) will be described.

[0038] The metal powder of the present invention is an aggregate of a plurality of metal particles.

[0039] In the metal powder of the present invention, the number ratio of particles having an aspect ratio of 0.4 or less and a maximum major diameter of 150 μm or greater is 0.30% or less based on the number of all particles constituting the metal powder of the present invention.

[0040] In the present application, a particle having an aspect ratio of 0.4 or less and a maximum length diameter of 150 μm or more is referred to as a "needle-shaped particle".

[0041] In the present application, the "aspect ratio" of a particle means the ratio of the minor axis diameter of the particle to the major axis diameter of the particle (minor axis diameter of the particle / major axis diameter of the particle). The more elongated the particle, the smaller the value of the aspect ratio of the particle.

[0042] In the present application, the "major axis diameter" and "minor axis diameter" of a particle mean the length of the major diameter and the minor diameter, respectively, when the particle is enclosed by two sets of parallel lines.

[0043] In the present application, the "maximum length diameter" of a particle means the maximum value among the distances between any two points on the outline of the particle.

[0044] In the present application, the number ratio (%) of needle-shaped particles is obtained based on the following formula.

[0045] Number ratio (%) of needle-shaped particles = (number of needle-shaped particles) / (number of all particles constituting the powder) x 100

[0046] Generally, the flowability of a metal powder can be confirmed based on JIS Z2502:2020. Specifically, by measuring the time (s / 50 g) required for 50 g of powder to fall from a hopper with the orifice at the lower end of the hopper opened, the flowability of the metal powder can be evaluated. The ease of handling of the metal powder in ordinary circumstances during the period when the nozzle is not clogged can be used as a standard for evaluating the flowability thereof.

[0047] However, when the flowability is evaluated using such a small amount of 50 g of test material, only the behavior of the powder in a short period of time of less than 20 seconds can be confirmed. Therefore, when evaluating whether the powder has long-term flowability, in particular, whether it has practical flowability suitable for the deposition method, it is preferable to evaluate it on a scale other than the flowability in ordinary circumstances.

[0048] Therefore, in the metal powder of the present application, the number ratio of needle-shaped particles, based on the number of all particles constituting the metal powder of the present application, is 0.30% or less. The number ratio of needle-shaped particles in the metal powder of the present application is preferably 0.25% or less, more preferably 0.20% or less, and further preferably 0.15% or less.

[0049] If the number ratio of needle-shaped particles is less than 0.01%, it takes a very long time to fractionate using a vibrating sieve device, and the productivity significantly decreases. Therefore, the number ratio of needle-shaped particles in the metal powder of the present application can be 0.01% or more. Alternatively, the number ratio of needle-shaped particles in the metal powder of the present application can be 0.02% or more. These lower limits can be combined with any of the aforementioned upper limits, respectively.

[0050] The number of particles and the shape of the particles can be analyzed, for example, using an image analysis device Morphologi G3 manufactured by Malvern. Specifically, first, the metal powder is scattered on a glass slide, and the shape of each particle is observed as a two-dimensional projection using an optical microscope, and the major axis diameter, the minor axis diameter, and the maximum length of each particle are obtained. Specifically, an image of each particle is captured, and the shape parameters are calculated by image analysis to obtain the major axis diameter, the minor axis diameter, and the maximum length of each particle. These steps can be automatically photographed and automatically analyzed by computer software, and thus the number and the shape of all the particles constituting the metal powder can be investigated. The number and the shape of tens of thousands of particles can also be investigated. Furthermore, the metal powder to be analyzed in terms of the number of particles and the shape of the particles is determined in relation to the mesh size of the sieve used in the classification. In one embodiment, the number of particles and the shape of the particles are analyzed with respect to the metal powder having a particle size of 45 μm or more.

[0051] The maximum value among the maximum lengths of all the particles constituting the metal powder of the present application is preferably 1000 μm or less. That is, the metal powder of the present application preferably does not contain particles having a maximum length of more than 1000 μm. This is because if the maximum length of the particles is too large, clogging of the nozzle is likely to occur. For example, even if the number ratio of the needle-shaped particles satisfies the criteria of the present application, if particles having a maximum length of more than 1000 μm are contained, even one particle can cause clogging of the nozzle. Therefore, the maximum value among the maximum lengths of all the particles constituting the metal powder of the present application is preferably 1000 μm or less, more preferably 370 μm or less, and further preferably 300 μm or less. The lower limit of the maximum value can be appropriately adjusted. The lower limit of the maximum value can be, for example, 100 μm or more, or 200 μm or more. These lower limits can be combined with any of the aforementioned upper limits.

[0052] When the metal powder of the present application is used in additive manufacturing by the deposition method, the median particle diameter D 50 of the metal powder of the present application is preferably 45 μm or more and 150 μm or less, more preferably 55 μm or more and 120 μm or less, and further preferably 60 μm or more and 90 μm or less.

[0053] The median particle diameter D 50 of the metal powder is the particle diameter at which the cumulative volume reaches 50% in a cumulative frequency distribution curve based on the volume, with the total volume of the metal powder being taken as 100%. The median particle diameter D 50Measured using the laser diffraction and scattering method. An example of a suitable instrument for this measurement is the Nikkiso Co., Ltd. laser diffraction and scattering particle size distribution analyzer, the "Microtrac MT3000." Powder and pure water are placed in the instrument's sample cell, and the particle size is measured based on the light scattering information from the particles.

[0054] Hereinafter, examples of the component composition of the metal powder of the present invention will be described.

[0055] Examples of the metal powder of the present invention include Ni-based alloy powder, Co-based alloy powder, Fe-based alloy powder, and Cu-based alloy powder.

[0056] [Ni-based alloy powder]

[0057] In one embodiment, the metal powder of the present invention is a Ni-based alloy powder. The Ni-based alloy powder may be composed of Ni and inevitable impurities, and in addition to Ni and inevitable impurities, may contain one or more elements selected from Fe, Cr, C, Mn, Si, Mo, Co, Nb, Al, Ti, and B. When the Ni-based alloy powder contains one or more elements selected from Fe, Cr, C, Mn, Si, Mo, Co, Nb, Al, Ti, and B, the balance of the Ni-based alloy powder is composed of Ni and inevitable impurities.

[0058] [Co-based alloy powder]

[0059] In one embodiment, the metal powder of the present invention is a Co-based alloy powder. The Co-based alloy powder may be composed of Co and inevitable impurities, and may also contain one or two elements selected from Cr and Mo in addition to Co and inevitable impurities. When the Co-based alloy powder contains one or two elements selected from Cr and Mo, the balance of the Co-based alloy powder is composed of Co and inevitable impurities.

[0060] [Fe-based alloy powder]

[0061] In one embodiment, the metal powder of the present invention is an Fe-based alloy powder. The Fe-based alloy powder may be composed of Fe and inevitable impurities, and in addition to Fe and inevitable impurities, may also contain one or more elements selected from Ni, Co, Mo, Ti, Al, Cr, Cu, and C. When the Fe-based alloy powder contains one or more elements selected from Ni, Co, Mo, Ti, Al, Cr, Cu, and C, the balance of the Fe-based alloy powder may be Fe and inevitable impurities.

[0062] [Cu-based alloy powder]

[0063] In one embodiment, the metal powder of the present invention is a Cu-based alloy powder. The Cu-based alloy powder may be composed of Cu and inevitable impurities, and may also contain Zr in addition to Cu and inevitable impurities. When the Cu-based alloy powder contains Zr, the balance of the Cu-based alloy powder is composed of Cu and inevitable impurities.

[0064] Hereinafter, an example of the method for producing the metal powder of the present invention will be described.

[0065] The metal powder of the present invention can be obtained by preparing a metal powder raw material having a predetermined component composition and classifying the prepared metal powder raw material.

[0066] Examples of the metal powder raw material include Ni-based alloy powder, Co-based alloy powder, Fe-based alloy powder, and Cu-based alloy powder. The descriptions of the Ni-based alloy powder, Co-based alloy powder, Fe-based alloy powder, and Cu-based alloy powder are the same as those above.

[0067] Various methods can be used to produce the metal powder raw material, but atomization is preferred. Among atomization methods, gas atomization is particularly preferred. In the gas atomization method, the raw material is placed in a container (quartz crucible) with fine holes in the bottom. The raw material is melted by high-frequency induction heating in an argon or nitrogen atmosphere. As the raw material melt flows out of the fine holes in the crucible, it is sprayed with high-speed argon or nitrogen gas, causing it to disperse and rapidly solidify, resulting in the metal powder raw material.

[0068] In one embodiment, the metal powder raw material is a gas atomized powder produced by a gas atomization method.

[0069] Metal powder raw material classification can be performed, for example, using a dry vibrating screen device. A vibrating screen device uses a motor, vibrator, or other device to vibrate a sieve (mesh screen), effectively screening the metal powder raw material on the sieve and selecting particles of a specified size from the metal powder raw material. To prevent clogging, bouncing balls are typically used to bounce on the sieve. These bouncing balls are made of polyurethane, for example. For example, the vibrating screen device (inner ring type) 502 manufactured by DALTON can be used.

[0070] In the classification of the metal powder raw material, after sieving to adjust the particle size, sieving to remove the needle-shaped particles is performed. Alternatively, sieving to remove the needle-shaped particles is performed, and then sieving to adjust the particle size is performed.

[0071] In the sieving for adjusting the particle size, first, sieving is performed on the metal powder raw material by the vibrating sieve device using a sieve with a large mesh size in the state where the rebounding balls are normally used, to obtain undersize. Next, sieving is performed on the undersize obtained above by the vibrating sieve device using a sieve with a small mesh size in the state where the rebounding balls are normally used, to obtain oversize. The oversize obtained is the metal powder of the prescribed particle size (small mesh size ~ large mesh size).

[0072] In the sieving for removing the acicular particles, it is preferable to reduce the vibration so as to suppress the acicular particles from standing up with the short axis diameter of the acicular particles oriented toward the direction of the mesh of the sieve, thereby causing the acicular particles to vertically pass through the mesh of the sieve. The sieving is performed in the state where the rebounding balls are not used or the number of the rebounding balls is reduced, and the classification efficiency is generally reduced, so it is not an easy step to take, but by intentionally not using the rebounding balls or reducing the number of the rebounding balls, it is possible to reduce the proportion of the acicular particles in the metal powder obtained by the sieving.

[0073] In the sieving for removing the acicular particles, in the state where the rebounding balls are not used or the number of the rebounding balls is reduced, sieving is performed on the metal powder obtained by the sieving for the particle size adjustment by the vibrating sieve device using a sieve with a large mesh size or a mesh size higher than that, to actively remove the acicular particles, to obtain undersize. The undersize obtained is the metal powder of the present application in which the proportion of the acicular particles is reduced.

[0074] In the sieving performed by the vibrating sieve device in the state where the rebounding balls are not used or the number of the rebounding balls is reduced, because the vibration is easily suppressed, there are no cases where the acicular particles are violently vibrated compared to the case where the rebounding balls are normally used. Therefore, it is possible to suppress the acicular particles from standing up with the short axis diameter of the acicular particles oriented toward the direction of the mesh of the sieve, thereby causing the acicular particles to vertically pass through the mesh of the sieve. That is, in the sieving in the state where the rebounding balls are not used or the number of the rebounding balls is reduced, it is possible to selectively remove the acicular particles with the major axis diameter larger than the mesh size of the sieve. In the sieving in the state where the rebounding balls are not used or the number of the rebounding balls is reduced, in order to remove the acicular particles, it is preferable to use a sieve with a larger mesh size than the sieve used in the sieving for the particle size adjustment. This is to prevent the particles other than the acicular particles from clogging and to improve the classification efficiency. In the sieving in the state where the rebounding balls are not used or the number of the rebounding balls is reduced, for example, a sieve with a nominal pore size of 150 μm can be used.

[0075] In one embodiment, the metal powder of the present invention is adjusted to a particle size of 45 to 125 μm by classifying the metal powder raw material for use in deposition-based additive manufacturing. The metal powder having a particle size of 45 to 125 μm can be obtained by sieving the metal powder raw material using a sieve with a nominal aperture of 125 μm. The resulting undersize fraction is then sieved using a sieve with a nominal aperture of 45 μm to obtain the oversize fraction, i.e., the metal powder having a particle size of 45 to 125 μm.

[0076] As an example of a specific classification procedure, the classification procedure for obtaining a metal powder having a particle size of 45 to 125 μm and a reduced ratio of the number of needle-shaped particles will be described below.

[0077] First, under the condition that bouncing balls are normally used, the metal powder raw material is screened by a vibrating screen device using a sieve with a nominal aperture of 125μm to obtain a screened material. Secondly, under the condition that bouncing balls are normally used, the screened material obtained above is screened by a vibrating screen device using a sieve with a nominal aperture of 45μm to obtain a screened material. Next, without using bouncing balls, the screened material obtained above is screened by a vibrating screen device using a sieve with a nominal aperture of 150μm to actively remove needle-shaped powder and obtain a screened material. The obtained screened material is a metal powder with a particle size of 45 to 125μm in which the number ratio of needle-shaped particles is reduced.

[0078] Hereinafter, the additively manufactured product of the present invention will be described.

[0079] The additively manufactured product of the present invention is an additively manufactured product obtained by additive manufacturing using a material for additive manufacturing containing the metal powder of the present invention.

[0080] Representative additive manufacturing methods include, for example, a powder bed method (powder bed fusion bonding method) and a deposition method (directed energy deposition method).

[0081] The material for additive manufacturing may contain materials other than the metal powder of the present invention (for example, a powder binder such as resin powder), but is preferably composed only of the metal powder of the present invention.

[0082] The material for additive manufacturing containing the metal powder of the present invention is suitable for additive manufacturing by a deposition method.

[0083] The porosity of the additively manufactured article of the present invention is preferably 0.14% or less, more preferably 0.12% or less, and even more preferably 0.06% or less. The lower limit of the porosity of the additively manufactured article of the present invention is preferably as low as possible.

[0084] The porosity of the additively manufactured product of the present invention can be calculated based on the following formula.

[0085] Porosity (%) = 100 (%) - relative density (%)

[0086] Relative density can be measured as follows. Using the weight of the additively manufactured object in air, its weight in water, and the density of water, calculate the density of the additively manufactured object (g / mm 3 The Archimedean density measurement method calculates the density of the additively manufactured object by dividing its weight in air by its volume (weight of the additively manufactured object in water / density of water at the measured temperature). Meanwhile, the density (g / mm2) of the powder used in the manufacture of the additively manufactured object is calculated by measuring the dry density using the constant volume expansion method (gas used: helium, device used: Micromeritics AccuPyc1330 manufactured by Shimadzu). 3 The relative density (%) of the additively manufactured body is calculated based on the following formula, according to the density of the additively manufactured body and the density of the powder.

[0087] Relative density of the additively manufactured body (%) = density of the additively manufactured body / density of the powder × 100

[0088] If the proportion of needle-shaped particles in the powder used in additive manufacturing increases, the amount of powder supplied from the powder supply nozzle decreases, thereby increasing the porosity of the additively manufactured product. If the proportion of needle-shaped particles is particularly high, the nozzle may become clogged mid-process, preventing powder supply and halting additive manufacturing. The metal powder of the present invention has a low proportion of needle-shaped particles, which minimizes the effect of poor flowability. Therefore, additive manufacturing using the metal powder of the present invention can produce dense additively manufactured products with low porosity.

[0089] Example

[0090] Hereinafter, embodiments of the present invention will be described.

[0091] <Production of Metal Powder Raw Materials>

[0092] Metal powder raw materials having the following composition were prepared by gas atomization. The percentages in the following composition are by mass.

[0093] [Ni-based alloy powder] Fe: 23%, Cr: 20%, C: 0.05%, Mn: 0.1%, Si: 0.2%, Mo: 3.0%, Co: 0.3%, Nb: 5.2%, Al: 0.5%, Ti: 0.9%, B: 0.003%, balance: Ni and inevitable impurities

[0094] [Co-based alloy powder] Cr: 28.0%, Mo: 6.0%, balance: Co and inevitable impurities (this powder is composed of a CoCrMo alloy)

[0095] [Fe-based alloy powder] Ni: 18.0%, Co: 9.0%, Mo: 4.9%, Ti: 0.7%, Al: 0.1%, Cr: 0.2%, Cu: 0.1%, C: 0.02%, balance: Fe and inevitable impurities (This powder is made of maraging steel)

[0096] [Cu-based alloy powder] Z: 1.0%, balance: Cu and unavoidable impurities (this powder is composed of a CuZr alloy)

[0097] As shown in Table 1, Ni-based alloy powder was used in Examples 1 and 2, Co-based alloy powder was used in Examples 3 and 4, Fe-based alloy powder was used in Examples 5 and 6, and Cu-based alloy powder was used in Examples 7 and 8. As shown in Table 2, Ni-based alloy powder was used in Comparative Examples 1 to 3, Co-based alloy powder was used in Comparative Examples 4 to 6, Fe-based alloy powder was used in Comparative Examples 7 to 9, and Cu-based alloy powder was used in Comparative Examples 10 to 12.

[0098] <Classification of Metal Powder Raw Materials>

[0099] The metal powder raw material is classified. Classification is performed using a dry vibrating screen device (DALTON Vibrating Screen (Inner Ring Type) 502). This classification of the metal powder raw material yields a metal powder with a particle size of 45 to 125 μm, with a reduced proportion of needle-shaped particles, for use in additive manufacturing using a deposition method. The specific classification steps are as follows.

[0100] First, under the condition that bouncing balls are usually used, the metal powder raw material is screened by a vibrating screen device using a sieve with a nominal aperture of 125μm to obtain a screened material. Secondly, under the condition that bouncing balls are usually used, the screened material obtained above is screened by a vibrating screen device using a sieve with a nominal aperture of 45μm to obtain a screened material. Next, under the condition that bouncing balls are not used, the screened material obtained above is screened by a vibrating screen device using a sieve with a nominal aperture of 150μm to actively remove needle-shaped particles and obtain a screened material. The obtained screened material is a metal powder with a particle size of 45 to 125μm in which the proportion of the number of needle-shaped particles is reduced.

[0101] <Evaluation of Metal Powder>

[0102] For a metal powder with a particle size of 45 to 125 μm and a reduced number of needle-shaped particles, the median particle size D is calculated according to the following method: 50The results are shown in Tables 1 and 2.

[0103] [Median particle size D 50 ]

[0104] Median particle size D 50 The particle size distribution was measured by a laser diffraction and scattering method using a laser diffraction and scattering particle size distribution measuring device "Microtrac MT3000" manufactured by Nikkiso Co., Ltd.

[0105] [Ratio of number of needle-shaped particles and maximum value of the longest diameter]

[0106] Particle counts and particle shape analysis were performed using a Morphologi G3 image analyzer manufactured by Malvern. First, metal powder was dispersed onto a glass slide. Using an optical microscope, the shapes of all particles constituting the metal powder were observed in two-dimensional projections to determine the major axis diameter, minor axis diameter, and maximum diameter of each particle. Specifically, images of each particle were captured, and shape parameters were calculated through image analysis to determine the major axis diameter, minor axis diameter, and maximum diameter of each particle. These steps can be automated using computer software for imaging and analysis.

[0107] [Fluidity]

[0108] The fluidity of metal powder is evaluated according to JIS Z2502:2020. Specifically, the flowability is evaluated by opening the lower opening of a funnel containing 50g of metal powder sample and measuring the time it takes for 50g of powder to fall from the funnel (s / 50g). The ease of handling of the metal powder under normal conditions, when the nozzle is not clogged, can be used as a criterion for evaluating its flowability.

[0109] <Production and Evaluation of Additively Manufactured Products>

[0110] Using a metal powder with a particle size of 45 to 125 μm and a reduced number of needle-shaped particles, a 10 mm square block was produced using a deposition-based 3D additive manufacturing device (Mitsubishi Heavy Industries, Ltd., LAMDA200).

[0111] The porosity of the resulting additively manufactured body was calculated based on the following formula. The results are shown in Tables 1 and 2.

[0112] Porosity (%) = 100 (%) - relative density (%)

[0113] The relative density is measured as follows. Using the weight of the additively manufactured object in air, its weight in water, and the density of water, the density of the additively manufactured object (g / mm 3(Archimedes density measurement method). In the Archimedean density measurement method, the density of the additive body is calculated by dividing the weight of the additive body in air by the volume of the additive body (=weight of the additive body in water / density of water at the measurement temperature). On the other hand, the density (g / mm2) of the powder used to produce the additive body is calculated by measuring the dry density using the constant volume expansion method (gas used: helium, device used: micromeritics AccuPyc1330 manufactured by SHIMADZU). 3 The relative density (%) of the additively manufactured body is calculated based on the following formula, according to the density of the additively manufactured body and the density of the powder.

[0114] Relative density of the additively manufactured body (%) = density of the additively manufactured body / density of the powder × 100

[0115]

Table 1

[0116]

[0117]

Table 2

[0118]

[0119] <Relationship between the ratio of needle-shaped particles and the porosity of the additively manufactured product>

[0120] As shown in Tables 1 and 2, as the proportion of needle-shaped particles increases, the powder supply from the powder supply nozzle decreases, resulting in an increase in the porosity of the additively manufactured product. When the proportion of needle-shaped particles is particularly high, the nozzle becomes clogged mid-process, preventing the supply of metal powder and halting additive manufacturing mid-process.

[0121] The metal powders of Examples 1 to 8 have a low proportion of needle-shaped particles and have little effect on deterioration of fluidity. Therefore, during additive manufacturing, dense additively manufactured bodies with low porosity can be obtained.

[0122] The metal powders of Comparative Examples 1 to 12 had a high proportion of needle-shaped particles, resulting in increased porosity in additively manufactured products compared to the metal powders of Examples 1 to 8. Furthermore, the metal powders of Comparative Examples 3, 6, 9, and 12 contained particles with a maximum major diameter exceeding 1000 μm, which caused clogging during additive manufacturing and prevented the production of additively manufactured products.

[0123] Industrial applicability

[0124] The metal powder of the present invention is suitable for use in additive manufacturing for three-dimensional additive manufacturing of metal parts, and is particularly suitable for use in additive manufacturing using a deposition method.

[0125] Description of Reference Signs

[0126] 1 sieve (mesh screen)

[0127] 2. The gaps between the meshes of the sieve

[0128] 3 needle-shaped particles

Claims

1. A metal powder for additive manufacturing, wherein: The number ratio of particles having an aspect ratio of 0.4 or less and a maximum major diameter of 150 μm or more is 0.30% or less based on the number of all particles constituting the powder.

2. The metal powder for additive manufacturing according to claim 1, wherein The maximum value among the maximum major diameters of all particles constituting the powder is 1000 μm or less.

3. The metal powder for additive manufacturing according to claim 1 or 2, wherein: The number ratio of particles having an aspect ratio of 0.4 or less and a maximum major diameter of 150 μm or less is 0.01% or more based on the number of all particles constituting the powder.

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